CI: Stop using parallel: matrix: for generating jobs

The main reason is that we currently can't use the needs keyword to
reference the jobs created via matrix. Let's define explicit jobs
to be more flexible.

.gitlab-ci.yml

@@ -10,39 +10,57 @@ stages:
   - build
   - deploy
 
-# Build Yocto BSPs
-.build-matrix: &build-matrix
-  - PLATFORM: mx8mm
+.bsp:build:
+  extends: .yocto-build-template
+  variables:
+    KAS_CONFIG: "kas/ktn-${PLATFORM}.yml:kas/series/${YOCTO_SERIES}.yml"
+  rules:
+    - if: $HEAD_BUILD == "1"
+      variables:
+        KAS_CONFIG: "${KAS_CONFIG}:kas/dev/head-${YOCTO_SERIES}.yml"
+    - when: on_success
+
+bsp:build:mx8mm:dunfell:
+  extends: .bsp:build
+  variables:
+    PLATFORM: mx8mm
     YOCTO_SERIES: dunfell
     TARGETS: "image-ktn-qt"
-  - PLATFORM: mx6ul
+
+bsp:build:mx6ul:dunfell:
+  extends: .bsp:build
+  variables:
+    PLATFORM: mx6ul
     YOCTO_SERIES: dunfell
     TARGETS: "image-ktn"
-  - PLATFORM: mp1
+
+bsp:build:mp1:dunfell:
+  extends: .bsp:build
+  variables:
+    PLATFORM: mp1
     YOCTO_SERIES: dunfell
     TARGETS: "image-ktn"
-  - PLATFORM: mx8mm
+
+bsp:build:mx8mm:kirkstone:
+  extends: .bsp:build
+  variables:
+    PLATFORM: mx8mm
     YOCTO_SERIES: kirkstone
     TARGETS: "image-ktn-qt"
-  - PLATFORM: mx6ul
-    YOCTO_SERIES: kirkstone
-    TARGETS: "image-ktn"
-  - PLATFORM: mp1
+
+bsp:build:mx6ul:kirkstone:
+  extends: .bsp:build
+  variables:
+    PLATFORM: mx6ul
     YOCTO_SERIES: kirkstone
     TARGETS: "image-ktn"
 
-bsp:build:
-  extends: .yocto-build-template
-  parallel:
-    matrix:
-      *build-matrix
+bsp:build:mp1:kirkstone:
+  extends: .bsp:build
   variables:
-    KAS_CONFIG: "kas/ktn-${PLATFORM}.yml:kas/series/${YOCTO_SERIES}.yml"
-  rules:
-    - if: $HEAD_BUILD == "1"
-      variables:
-        KAS_CONFIG: "${KAS_CONFIG}:kas/dev/head-${YOCTO_SERIES}.yml"
-    - when: always
+    PLATFORM: mp1
+    YOCTO_SERIES: kirkstone
+    TARGETS: "image-ktn"
 
 # Build Container Image
 .container-vars: &container-vars